The present invention is directed to a sizing composition and sized fibers useful as reinforcement for polymers. More particularly, the present invention is directed to a sizing composition for glass fibers to produce sized glass fibers with improved performance in polymeric compounds, and with improved processability, and with improved handling characteristics.
Reinforced thermosetting unsaturated polyester based molding compounds can be produced with several forms of glass fiber reinforcement. These types include roving, continuous strand, chopped fibers, mat, and woven fabrics, and the like. Reinforced thermosetting plastic composites produced from thermosetting molding compounds like bulk molding compounds, and sheet molding compounds typically have about 15 to 25 and 25 to 45 percent glass fiber content respectively. In bulk molding compounds, the fibrous reinforcement is usually in the form of randomly dispersed short fibers generally of length of about 1/4 inch to 1 inch. The short fibers can be produced from continuous strand that has contacted the unsaturated polyester resin or resin system and subsequently chopped into short lengths. In the sheet molding compounds, sometimes known as "prepreg" (preimpregnated mat) the fibrous reinforcement is present either as a continuous filament, chopped strand mat, or as chopped fibers deposited on a supporting carier, the fiber filler is impregnated with the unsaturated polyester resin system giving rise to sheets of molding compound in which the fibers have not been subjected to the degradating action of conventional molding compound mixtures. In addition to the conventional composites formed from bulk molding compounds and sheet molding compounds, molding compounds with higher amounts of fiber reinforcement can also be used in producing composites. Two families of fiber glass reinforced molding sheets that have recently been commercialized are the XMC.RTM. composites and the HMC.RTM. composites available from PPG Industries, Inc., Pittsburgh, Pennsylvania. These composites have high strength for structural uses. The HMC.RTM. composites offer isotropic strength properties approaching twice those of conventional sheet molding compound, by employing high glass fiber content with little or no filler. The XMC.RTM. composites are directionally oriented, moldable, resin-glass fiber sheets containing 65 to 75 percent continuous reinforcement.
Glass fibers used as reinforcement for thermosetting molding, compounds are formed by being drawn at high rates of speed from molten cones of glass formed at the tips of small orifices in a platinum device called a bushing. In order to protect the glass fibers from interfilament abrasion during formation and further processing and to make them compatible with the polymeric materials used in the thermosetting molding compounds, a sizing composition is applied to the fibers during their formation.
The sizing compositions used to obtain acceptable fiber glass reinforced molding composites generally contain lubricants, film-formers, coupling agents, wetting agents, emulsifiers and the like. The solubility of the glass fiber sizing composition in ethylenically unsaturated organic solvents can affect the final properties of the molded product, since a myriad of applications of thermosetting molding composites utilize unsaturated polyesters or vinylester resins. For example, in the process of producing sheet molding compound reinforcement in the form of glass fiber mat, chopped glass fibers, and continuous glass fiber roving, the reinforcement comes in contact with the resin system which is usually an unsaturated polyester resin system. The glass reinforced resin system is heated to and maintained at an elevated temperature and is transported by a carrier like polyethylene or cellulose films or sheets which are present above and below the resin system. When the reinforcement is in the form of chopped glass fibers, the chopped glass fibers come to rest on the moving film of resin covered polyethylene or cellulose and another layer of resin system is placed onto the chopped reinforcement along with another sheet or carrier and this sandwiched sheet molding compound is fed through compression rollers to effect impregnation of the glass by the resin mix and to distribute the resin, then the composite is rolled in packages of desired length. When the reinforcement is glass fiber mat, it is contacted with the resin system and is interleaved between polyethylene or cellulose sheets and passed through the compression rolls. Any further kneading or compression, if required, can be performed by ribbed rollers.
During the operation of producing a molding compound like sheet molding compound, the glass fiber reinforcement in any form is subjected to a multitude of forces and conditions that may tend to cause glass fibers to filamentize or become separated and possibly reduce the association of the strand with the resin. The affects of the filamentizing and reduced association are poor performance in the molding, cyclability, flow and solubility of the glass fiber reinforcement in the molding compound. Also affected would be the dispersion of the glass fiber reinforcement in the resin where the molding compound formed from the unsaturated polyester and the glass fiber reinforcement has good homogeneity which is usually referred to as "wet-through" or "flow-through". It is desirable to have a high degree of wet-through in a bulk molding compound, sheet molding compound and the HMC.RTM. composites and the XMC.RTM. composites, in order that the final physical properities of the composites and the processability thereof is at their maximum levels. Also, the association of the glass fibers with the resin usually referred to as "wet-out" during compounding means that the resin encapsulates the glass fibers and no bare glass is visible throughout the formed, molded compound. Wet-out during compounding is in measure the apparent intimacy of contact between the resin matrix and the glass fibers. If the glass fibers are not immediately wet-out following compounding, it is expected that they will wet-out on aging due to the increase in the viscosity of the compound. This leads to adverse effects on the processability, molding characteristics, and surface properties of the final molded article or composite.
It is an object of the present invention to provide a sizing composition to give glass fiber improved integrity in order that they remain intact during processing to produce reinforced molding compounds and composites therefrom.
It is a further object of the invention to provide a sizing composition to give glass fibers that when used as reinforcement in molding compounds enables production of the molding compounds at good molding rates, with good cycle times, with good flow-through, and with good wet-out properties.
It is a further additional object of the present invention to provide a sizing composition which yields sized glass fibers having improved integrity between the glass fibers and the polyester resin, or vinylester resin, or epoxy resin of a thermosetting molding compound in the production of thermosetting molding sheet composites.
It is another object of the present invention to provide a sizing composition for use with glass fibers that yields sized glass fibers for use in thermosetting molding compounds, wherein the sized glass fibers are produced with improved processability and have improved handling characteristics.